import re
import sys
import os
from datetime import timedelta

def format_timestamp(timestamp):
  hours, remainder = divmod(timestamp.total_seconds(), 3600)
  minutes, seconds = divmod(remainder, 60)
  milliseconds = timestamp.microseconds // 1000
  return f"{int(hours):02d}:{int(minutes):02d}:{int(seconds):02d},{int(milliseconds):03d}"

def lrc_to_srt(lrc_filename, srt_filename):
  with open(lrc_filename, 'r', encoding='utf-8') as lrc_file:
    lrc_content = lrc_file.readlines()

  srt_content = []
  subtitle_counter = 1
  previous_end_time = None

  for i, line in enumerate(lrc_content):
    match = re.match(r'\[(\d{2}):(\d{2})\.(\d{2})\](.*)', line)
    ## Explanation to the regex:
    ## \[           (\d{2})             :       (\d{2})             \.    (\d{2})               \]        (.*)
    ## bracket      minutes (2 digits)  colon   seconds (2 digits)  dot   millisecs (2 digits)  bracket   lyrical line (can be blank)
    if match:
      print(f'debug: matched line {line.strip()}')
      start_minutes = int(match.group(1))
      start_seconds = int(match.group(2))
      start_milliseconds = int(match.group(3)) * 10
      print(f'matched text: {match.group(4)}')

      start_time = timedelta(minutes=start_minutes, seconds=start_seconds, milliseconds=start_milliseconds)
      if len(srt_content) > 0:
        # srt_content[-1] += f"{format_timestamp(start_time - timedelta(milliseconds=1))}\n"
        srt_content[-1] += f"{format_timestamp(start_time)}\n"
        srt_content.append(f"{subtitle_text}\n\n")

      srt_content.append(f"{subtitle_counter}\n")
      srt_content.append(f"{format_timestamp(start_time)} --> ")

      subtitle_text = match.group(4).strip()
      subtitle_counter += 1
      previous_end_time = start_time

  if previous_end_time is not None:
    srt_content[-1] += f"{format_timestamp(previous_end_time)}\n"
    srt_content.append(f"{subtitle_text}\n\n")
    

  with open(srt_filename, 'w', encoding='utf-8') as srt_file:
    srt_file.writelines(srt_content)

  print(f"Conversion from LRC to SRT completed. SRT file saved as '{srt_filename}'.")

if __name__ == "__main__":
  if not(len(sys.argv) == 3 or len(sys.argv) == 2):
    print("Usage: python lrc2srt.py <input_lrc_file> <output_srt_file>")
    print("or: python lrc2srt.py <input_lrc_file>")
    print("If no output file name is supplied, the input file name will be used by default.")
  else:
    lrc_filename = sys.argv[1]
    if len(sys.argv) == 3:
      srt_filename = sys.argv[2]
    else:
      raw_filename, ext = os.path.splitext(lrc_filename)
      srt_filename = raw_filename + '.srt'  
    lrc_to_srt(lrc_filename, srt_filename)